Structural determinants of allosteric antagonism at metabotropic glutamate receptor 2: mechanistic studies with new potent negative allosteric modulators

BACKGROUND AND PURPOSE

Altered glutamatergic neurotransmission is linked to several neurological and psychiatric disorders. Metabotropic glutamate receptor 2 (mGlu₂) plays an important role on the presynaptic control of glutamate release and negative allosteric modulators (NAMs) acting on mGlu₂/₃ receptors are under assessment for their potential as antidepressants, neurogenics and cognitive enhancers. Two new potent mGlu₂/₃ NAMs, RO4988546 and RO5488608, are described in this study and the allosteric binding site in the transmembrane (TM) domain of mGlu₂ is characterized.

EXPERIMENTAL APPROACH

Site directed mutagenesis, functional measurements and β₂-adrenoceptor-based modelling of mGlu₂ were employed to identify important molecular determinants of two new potent mGlu₂/₃ NAMs.

KEY RESULTS

RO4988546 and RO5488608 affected both [³H]-LY354740 agonist binding at the orthosteric site and the binding of a tritiated positive allosteric modulator (³H-PAM), indicating that NAMs and PAMs could have overlapping binding sites in the mGlu₂ TM domain. We identified eight residues in the allosteric binding pocket that are crucial for non-competitive antagonism of agonist-dependent activation of mGlu₂ and directly interact with the NAMs: Arg³·²⁸, Arg³·²⁹, Phe³·³⁶, His(E2.52) , Leu⁵·⁴³, Trp⁶·⁴⁸, Phe⁶·⁵⁵ and Val⁷·⁴³. The mGlu₂ specific residue His(E2.52) is likely to be involved in selectivity and residues located in the outer part of the binding pocket are more important for [³H]-LY354740 agonist binding inhibition, which is independent of the highly conserved Trp⁶·⁴⁸ residue.

CONCLUSIONS AND IMPLICATIONS

This is the first complete molecular investigation of the allosteric binding pocket of mGlu₂ and Group II mGluRs and provides new information on what determines mGlu₂ NAMs selective interactions and effects.

miR-296 regulation of a cell polarity-cell plasticity module controls tumor progression

The expression of small, non-coding RNA or microRNAs (miR), is frequently deregulated in human cancer, but how these pathways affect disease progression is still largely elusive. Here, we report on a miR, miR-296, which is progressively lost during tumor progression and correlates with metastatic disease in colorectal, breast, lung, gastric, parathyroid, liver and bile ducts cancers. Functionally, miR-296 controls a global cell motility gene signature in epithelial cells by transcriptionally repressing the cell polarity-cell plasticity module, Scribble (Scrib). In turn, loss of miR-296 causes aberrantly increased and mislocalized Scrib in human tumors, resulting in exaggerated random cell migration and tumor cell invasiveness. Re-expression of miR-296 in MDA-MB231 cells inhibits tumor growth in vivo. Finally, miR-296 or Scrib levels predict tumor relapse in hepatocellular carcinoma patients. These data identify miR-296 as a global repressor of tumorigenicity and uncover a previously unexplored exploitation of Scrib in tumor progression in humans.

Visceral artery aneurysms in liver transplant candidates and in patients after liver transplantation

There are only few reviews concerning visceral aneurysms in cirrhotics, and a small number of papers on visceral aneurysms in liver transplant patients. The present paper investigates this condition in both groups of patients in a 10-year-retrospective study.

Microvesicles derived from human adult mesenchymal stem cells protect against ischaemia-reperfusion-induced acute and chronic kidney injury

BACKGROUND

Several studies demonstrated that mesenchymal stem cells (MSCs) reverse acute kidney injury (AKI) by a paracrine mechanism rather than by MSC transdifferentiation. We recently demonstrated that microvesicles (MVs) released from MSCs may account for this paracrine mechanism by a horizontal transfer of messenger RNA and microRNA.

METHODS

MVs isolated from MSCs were injected intravenously in rats (30 μg/rat) immediately after monolateral nephrectomy and renal artery and vein occlusion for 45 min. To evaluate the MV effects on AKI induced by ischaemia-reperfusion injury (IRI), the animals were divided into different groups: normal rats (n = 4), sham-operated rats (n = 6), IRI rats (n = 6), IRI + MV rats (n = 6), and IRI + RNase-MV rats (n = 6), and all animals were sacrificed at Day 2 after the operation. To evaluate the chronic kidney damage consequent to IRI, the rats were divided into different groups: sham-operated rats (n = 6) and IRI rats (n = 6), IRI + MV rats (n = 6), and all animal were sacrificed 6 months after the operation.

RESULTS

We found that a single administration of MVs, immediately after IRI, protects rats from AKI by inhibiting apoptosis and stimulating tubular epithelial cell proliferation. The MVs also significantly reduced the impairment of renal function. Pretreatment of MVs with RNase to inactivate their RNA cargo abrogated these protective effects. Moreover, MVs by reducing the acute injury also protected from later chronic kidney disease.

CONCLUSION

MVs released from MSCs protect from AKI induced by ischaemia reperfusion injury and from subsequent chronic renal damage. This suggest that MVs could be exploited as a potential new therapeutic approach.

The melanocortin system in control of inflammation

Melanocortin peptides, the collective term for α-, β-, and γ-melanocyte-stimulating hormone (α-, β-, γ-MSH) and adrenocorticotropic hormone (ACTH), are elements of an ancient modulatory system. Natural melanocortins derive from the common precursor pro-opiomelanocortin (POMC). Five receptor subtypes for melanocortins (MC₁-MC₅) are widely distributed in brain regions and in peripheral cells. Melanocortin receptor activation by natural or synthetic ligands exerts marked anti-inflammatory and immunomodulatory effects. The anticytokine action and the inhibitory influences on inflammatory cell migration make melanocortins potential new drugs for treatment of inflammatory disorders. Effectiveness in treatment of acute, chronic, and systemic inflammatory disorders is well documented in preclinical studies. Further, melanocortins are promising compounds in neuroprotection. This review examines the main signaling circuits in anti-inflammatory and immunomodulatory actions of melanocortins, and the potential therapeutic use of these molecules.

Use of a rotary bioartificial liver in the differentiation of human liver stem cells

The use of bioartificial livers (BALs) for the expansion of human adult liver stem cells and the production of growth factors could be a potential strategy for cell-based extracorporeal liver support. The present study aimed to assessing the differentiation of human adult liver stem cells in a rotary BAL. Liver stem cells were seeded into a polysulphone membrane filter at a density of 3 x 10(8) cells, and the filter was connected to a rotary bioreactor perfusion system (37 degrees C, 50 mL/min, 48 h). Viability, cell differentiation, and metabolic performances were evaluated at 24 and 48 h. Hepatocyte growth factor production from human adult liver stem cells, mature hepatocytes, and mesenchymal stem cells in adhesion and in the rotary BAL conditions was compared. Liver stem cells cultured in the rotary BAL produced the highest amounts of albumin (p = 0.002) and ammonia-induced urea (p = 0.0001), and had an increased cytochrome P450 expression in respect to liver stem cells in adhesion. Remarkably, liver stem cells in the rotary BAL produced very high amounts of hepatocyte growth factor (p = 0.005) in respect to hepatocytes and mesenchymal stem cells. Moreover, the cells lost their stem cell markers and acquired several markers of mature hepatocytes. In conclusion, the rotary BAL favored liver stem cell differentiation into mature hepatocyte-like cells.

Growth factors and tendon healing

Recent attention has focused on the biological pathways by which tendons heal leading to the identification of some growth factors (GFs) with involvement in this process. No studies have been published on the time course of the various GFs during tendon healing process in vivo, in humans. We review what is known about these GFs and their role in tendon healing.

The peptide NDP-MSH induces phenotype changes in the heart that resemble ischemic preconditioning

alpha-Melanocyte-stimulating hormone (alpha-MSH) is a pro-opiomelanocortin (POMC)-derived peptide that exerts multiple protective effects on host cells. Previous investigations showed that treatment with alpha-MSH or synthetic melanocortin agonists reduces heart damage in reperfusion injury and transplantation. The aim of this preclinical research was to determine whether melanocortin treatment induces preconditioning-like cardioprotection. In particular, the plan was to assess whether melanocortin administration causes phenotype changes similar to those induced by repetitive ischemic events. The idea was conceived because both ischemic preconditioning and melanocortin signaling largely depend on cAMP response element binding protein (CREB) phosphorylation. Rats received single i.v. injections of 750microg/kg of the alpha-MSH analogue Nle(4),DPhe(7)-alpha-MSH (NDP-MSH) or saline and were sacrificed at 0.5, 1, 3, or 5h. Western blot analysis showed that rat hearts expressed melanocortin 1 receptor (MC1R) protein. Treatment with NDP-MSH was associated with early and marked increase in interleukin 6 (IL-6) mRNA. This was followed by signal transducer and activator of transcription 3 (STAT3) phosphorylation and induction of suppressor of cytokine signaling 3 (SOCS3). There were no changes in expression of other cytokines of the IL-6 family. Expression of IL-10, IL-1beta, and TNF-alpha was likewise unaltered. In hearts of rats treated with NDP-MSH there was increased expression of the orphan nuclear receptor Nur77. The data indicate that NDP-MSH induces phenotype changes that closely resemble ischemic preconditioning and likely contribute to its established protection against reperfusion injury. In addition, the increased expression of Nur77 and SOCS3 could be part of a broader anti-inflammatory effect.

Iron-dependent regulation of MDM2 influences p53 activity and hepatic carcinogenesis

Iron overload is a risk factor for hepatocarcinoma, but the pathways involved are poorly characterized. Gene expression analysis in immortalized mouse hepatocytes exposed to iron or the iron chelator deferoxamine revealed that iron downregulated, whereas deferoxamine upregulated, mRNA levels of mouse double minute gene 2 (MDM2), the ubiquitin ligase involved in the degradation of the oncosuppressor p53. Regulation of MDM2 by iron status was observed at protein levels in mouse hepatocytes and rat liver, and was associated with specular changes in p53 expression. Iron dependent regulation of MDM2/p53 was confirmed ex-vivo in human monocytes, by manipulation of iron pool and in a genetic model of iron deficiency, leading to modulation of p53 target genes involved in the antioxidant response and apoptosis. Iron status influenced p53 ubiquitination and degradation rate, and the MDM2 inhibitor nutlin increased p53 levels in iron-depleted cells. Furthermore, nutlin enhanced the antiproliferative activity of deferoxamine in HepG2 hepatoblastoma cells. The MDM2 -309T > G promoter polymorphism, determining increased MDM2 and lower p53 activity, was associated with higher risk of hepatocarcinoma in cirrhotic patients with hemochromatosis, and with HFE mutations in patients with hepatocarcinoma without hemochromatosis, suggesting an interaction between MDM2 and iron in the pathogenesis of hepatocarcinoma. In conclusion, iron status influences p53 activity and antioxidant response by modulating MDM2 expression. MDM2 inhibitors may enhance the antiproliferative activity of iron chelators.

Iron-dependent regulation of MDM2 influences p53 activity and hepatic carcinogenesis

Iron overload is a risk factor for hepatocarcinoma, but the pathways involved are poorly characterized. Gene expression analysis in immortalized mouse hepatocytes exposed to iron or the iron chelator deferoxamine revealed that iron downregulated, whereas deferoxamine upregulated, mRNA levels of mouse double minute gene 2 (MDM2), the ubiquitin ligase involved in the degradation of the oncosuppressor p53. Regulation of MDM2 by iron status was observed at protein levels in mouse hepatocytes and rat liver, and was associated with specular changes in p53 expression. Iron dependent regulation of MDM2/p53 was confirmed ex-vivo in human monocytes, by manipulation of iron pool and in a genetic model of iron deficiency, leading to modulation of p53 target genes involved in the antioxidant response and apoptosis. Iron status influenced p53 ubiquitination and degradation rate, and the MDM2 inhibitor nutlin increased p53 levels in iron-depleted cells. Furthermore, nutlin enhanced the antiproliferative activity of deferoxamine in HepG2 hepatoblastoma cells. The MDM2 -309T > G promoter polymorphism, determining increased MDM2 and lower p53 activity, was associated with higher risk of hepatocarcinoma in cirrhotic patients with hemochromatosis, and with HFE mutations in patients with hepatocarcinoma without hemochromatosis, suggesting an interaction between MDM2 and iron in the pathogenesis of hepatocarcinoma. In conclusion, iron status influences p53 activity and antioxidant response by modulating MDM2 expression. MDM2 inhibitors may enhance the antiproliferative activity of iron chelators.

Iron-dependent regulation of MDM2 influences p53 activity and hepatic carcinogenesis

Iron overload is a risk factor for hepatocarcinoma, but the pathways involved are poorly characterized. Gene expression analysis in immortalized mouse hepatocytes exposed to iron or the iron chelator deferoxamine revealed that iron downregulated, whereas deferoxamine upregulated, mRNA levels of mouse double minute gene 2 (MDM2), the ubiquitin ligase involved in the degradation of the oncosuppressor p53. Regulation of MDM2 by iron status was observed at protein levels in mouse hepatocytes and rat liver, and was associated with specular changes in p53 expression. Iron dependent regulation of MDM2/p53 was confirmed ex-vivo in human monocytes, by manipulation of iron pool and in a genetic model of iron deficiency, leading to modulation of p53 target genes involved in the antioxidant response and apoptosis. Iron status influenced p53 ubiquitination and degradation rate, and the MDM2 inhibitor nutlin increased p53 levels in iron-depleted cells. Furthermore, nutlin enhanced the antiproliferative activity of deferoxamine in HepG2 hepatoblastoma cells. The MDM2 -309T > G promoter polymorphism, determining increased MDM2 and lower p53 activity, was associated with higher risk of hepatocarcinoma in cirrhotic patients with hemochromatosis, and with HFE mutations in patients with hepatocarcinoma without hemochromatosis, suggesting an interaction between MDM2 and iron in the pathogenesis of hepatocarcinoma. In conclusion, iron status influences p53 activity and antioxidant response by modulating MDM2 expression. MDM2 inhibitors may enhance the antiproliferative activity of iron chelators.

Detrimental consequences of brain injury on peripheral cells

Acute brain injury and brain death exert detrimental effects on peripheral host cells. Brain-induced impairment of immune function makes patients more vulnerable to infections that are a major cause of morbidity and mortality after stroke, trauma, or subarachnoid hemorrhage (SAH). Systemic inflammation and organ dysfunction are other harmful consequences of CNS injury. Brain death, the most severe consequence of brain injury, causes inflammatory changes in peripheral organs that can contribute to the inferior outcome of organs transplanted from brain-dead donors. Understanding of the mechanisms underlying the detrimental effects of brain injury on peripheral organs remains incomplete. However, it appears that sympathetic nervous system (SNS)-activation contributes to elicit both inflammation and immunodepression. Indeed, norepinephrine (NE)-induced production of chemokines in liver and other organs likely participates in local and systemic inflammatory changes. Conversely, catecholamine-stimulated interleukin-10 (IL-10) production by blood monocytes exerts immunosuppressive effects. Activation of the hypothalamic-pituitary-adrenal axis (HPA) by increased inflammatory cytokines within the brain is a significant component in the CNS-induced immune function inhibition. Non-neurologic consequences of brain injury show impressive similarities regardless of the brain insult and appear to depend on altered neuroimmune circuits. Modulation of these circuits could reduce extra-brain damage and improve patient outcome in both vascular and traumatic brain injury.

Human liver stem cell-derived microvesicles accelerate hepatic regeneration in hepatectomized rats

Several studies indicate that adult stem cells may improve the recovery from acute tissue injury. It has been suggested that they may contribute to tissue regeneration by the release of paracrine factors promoting proliferation of tissue resident cells. However, the factors involved remain unknown. In the present study we found that microvesicles (MVs) derived from human liver stem cells (HLSC) induced in vitro proliferation and apoptosis resistance of human and rat hepatocytes. These effects required internalization of MVs in the hepatocytes by an alpha(4)-integrin-dependent mechanism. However, MVs pre-treated with RNase, even if internalized, were unable to induce hepatocyte proliferation and apoptosis resistance, suggesting an RNA-dependent effect. Microarray analysis and quantitative RT-PCR demonstrated that MVs were shuttling a specific subset of cellular mRNA, such as mRNA associated in the control of transcription, translation, proliferation and apoptosis. When administered in vivo, MVs accelerated the morphological and functional recovery of liver in a model of 70% hepatectomy in rats. This effect was associated with increase in hepatocyte proliferation and was abolished by RNase pre-treatment of MVs. Using human AGO2, as a reporter gene present in MVs, we found the expression of human AGO2 mRNA and protein in the liver of hepatectomized rats treated with MVs. These data suggested a translation of the MV shuttled mRNA into hepatocytes of treated rats. In conclusion, these results suggest that MVs derived from HLSC may activate a proliferative program in remnant hepatocytes after hepatectomy by a horizontal transfer of specific mRNA subsets.

Efficacy of low-dose GnRH analogue (Buserelin) in the treatment of hirsutism

The aim of the present study was to evaluate the effect of low dose GnRH analogue (Buserelin) on gonadal steroid secretion and hair growth in hirsute women. The drug was administered as a nasal spray (200 micrograms tid) to reduce gonadal steroid secretion. Eight hirsute women were treated for six month with the gonadotropin-releasing hormone analog. All had subclinical polycystic ovary syndromes on the basis of ultrasound or hormonal data, together with ovary dysfunctions and irregular menses. None had adrenal or pituitary dysfunction. The score of hirsutism was evaluated according to Ferriman and Gallway; pituitary function was evaluated measuring the FSH and LH response to GnRH stimulation and gonadal steroid secretion by measuring estradiol, progesterone, total plasma testosterone, androstenedione and androstanediol. Sex hormone binding globulin, insulin, prolactin and DHEA-S were also measured. The suppression of ovarian steroid secretion was confirmed by reductions in total plasma testosterone, and rostenedione and androstanediol that were detectable after one month of treatment. FSH and LH responses to GnRH stimulation were inhibited consistent with pituitary desensitization. No significant side effects were observed and all patients completed the trial. The score of hirsutism was 24 +/- 5 before, 19.6 +/- 6 by the 3rd month and 16.8 +/- 5.1 by the 6th month of treatment (p < 0.001); the effect was still evident 1 and 6 months after the withdrawal of the therapy (14.8 +/- and 15.8 +/- 5 respectively; p < 0.001). Our findings indicate that Buserelin is useful in the treatment of non adrenal hirsutism when other forms of therapy are contraindicated or poorly tolerated by the patient.